Semiconductor with through-substrate interconnect

ABSTRACT

Semiconductor devices are described that have a metal interconnect extending vertically through a portion of the device to the back side of a semiconductor substrate. A top region of the metal interconnect is located vertically below a horizontal plane containing a metal routing layer. Method of fabricating the semiconductor device can include etching a via into a semiconductor substrate, filling the via with a metal material, forming a metal routing layer subsequent to filling the via, and removing a portion of a bottom of the semiconductor substrate to expose a bottom region of the metal filled via.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application No. 14/755,274filed Jun. 30, 2015, which is a divisional of U.S. application Ser. No.13/850,840 filed Mar. 26, 2013, which is a divisional of U.S.application Ser. No. 13/160,363 filed Jun. 19, 2008, now U.S. Pat. No.8,404,587, which is a divisional of U.S. application Ser. No. 12/142,251filed Jun. 19, 2008, now U.S. Pat. No. 7,968,460, each of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor devices. Inparticular, the present disclosure relates to conductive interconnectsin semiconductor devices.

BACKGROUND

During fabrication of semiconductor devices a wafer of base material,such as crystalline silicon, is used to form electrical components. Theprocess steps to form the semiconductor device are generally additive orsubtractive steps. These can include, but are not limited to, growingmaterials, depositing materials, implanting ions, planarizing a surface,and etching material. These processes are performed on the wafer whichis then singulated into separate semiconductor die. Each die includes anactive surface, or top surface, where the process steps are performed toform the electrical devices, and a back surface.

After singulation, the semiconductor die can be packaged for use inother devices, such as consumer electronic products. Several methodshave been used to form electrical connections with the semiconductoractive surface, such as wire bonding and ball bonding. As an example,one process for packaging a semiconductor die includes (a) forming diceon a semiconductor wafer, (b) cutting the wafer to separate or singulatethe dice, (c) attaching individual die to an interposer substrate, (d)wire-bonding conductive bond-pads of the active surface of the die toterminals of the interposer substrate, and (e) encapsulating the diewith a suitable moulding compound.

In response to the desire to increase the density of semiconductordevices for a given footprint, semiconductor manufacturers have workedto develop ways to stack one or more devices on top of another.Different methods for electrically connecting the semiconductor dietogether have been described. These methods can include forming backside conductive interconnect locations. Some examples of backsideinterconnects are described in U.S. Pat. Nos. 6,582,992, 6,903,443,6,962,867 and 7,091,124.

For example, the U.S. Pat. No. 7,091,124 describes forming vias orpassages through a die and a bond-pad on an active surface of the die toa back side of the die. The U.S. Pat. No. 6,962,867 describes asemiconductor substrate including one or more vias having conductivematerial formed therein and which extend from an active surface to aback surface of the semiconductor substrate. A method for fabricatingsemiconductor components and interconnects, described in the U.S. Pat.No. 6,903,443 includes the steps of providing a substrate, such as asemiconductor die, forming external contacts on opposing sides of thesubstrate by laser drilling vias through the substrate, and formingconductive members in the vias. The U.S. Pat. No. 6,582,992 describesconductive grooves formed on the edges of a die that function asinterlevel conductors for a stacked die package.

Forming vias after the semiconductor processing is substantiallycomplete can be referred to as a via-last process. In contrast, somedevelopment work has been done to form the via prior to integrationprocessing, a via-first process. For example, a polysilicon via processwas disclosed in “A 3D Stacked Memory Integrated on a Logic Device UsingSMAFTI Technology,” Kurita, et al., 2007 Electronic Components andTechnology Conference, pages 821-829. The paper describes a via-firstprocess with a highly doped poly-Si as the filling material for throughsilicon vias in DRAM dice. The Si substrate etching and filling arecarried out before the DRAM device process in the via-first process. Thepaper indicates that the choice of poly-Si as the filling material canprevent metal atom contamination and temperature restriction in thedevice process that follow. As described in the paper, a trench isetched into a silicon substrate and the trench side-wall is isolatedwith thermal oxide. Poly-Si is deposited by Chemical Vapor Deposition(CVD) and the silicon surface is planarized with Chemical MechanicalPolishing (CMP) to remove excess layers at the top surface. A DRAMdevice process is then carried out on the wafer.

For reasons which will become apparent to those skilled in the art uponreading and understanding the present specification, there is a need inthe art for alternative methods and devices that provide back sideconductive interconnect locations for semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-section representation of a simplifiedsemiconductor device according to one embodiment of the invention;

FIGS. 2-14 are partial cross-section views of a simplified in-processsemiconductor according to embodiments of the invention;

FIGS. 15-16 are partial cross-section views of a simplified in-processsemiconductor according to embodiments of the invention; and

FIG. 17 illustrates a partial cross-section view of a simplifiedin-process semiconductor with a redistribution layer according anembodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description of the present embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the embodiments may be practiced. These embodiments are describedin sufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that process, chemical, or electrical changes may be madewithout departing from the scope of the present disclosure. The termswafer and substrate used previously and in the following descriptioninclude any base semiconductor structure. Furthermore, when reference ismade to a wafer or substrate in the following description, previousprocess steps may have been utilized to form regions/junctions in thebase semiconductor structure. In addition, directional references, e.g.,upper, lower, top, bottom and sides, are relative to one another andneed not refer to an absolute direction. The following detaileddescription is, therefore, not to be taken in a limiting sense.

The present disclosure describes semiconductor processes thatincorporate metal conductive interconnects into the fabrication processof an integrated circuit. As explained in greater detail below, theprocesses allow for the formation of metal filled vias during thefabrication of the semiconductor. The vias are formed and filledsubsequent to transistor formation and prior to the fabrication of metalrouting layers. Numerous benefits are achieved by the disclosedembodiments of the present invention, including tighter pitch viaformation, lower resistance than poly-Si interconnects, and an improvedintegration into semiconductor fabrication operations.

Referring to the illustrated cross-sectioned representation of asimplified semiconductor device 100 in FIG. 1, the semiconductorincludes a front side 102 and a back side 104. As known to those skilledin the art, electronic devices 106 are fabricated on and/or in asubstrate 108 generally on the top, or active, side of the semiconductorsubstrate. As described in detail below, a metal interconnect 110 isfabricated into the substrate 108 at a time in the semiconductorfabrication process after formation of some electronic devices 106, suchas transistors, but prior to fabrication of some metal routing layers112 and 114. Some semiconductor devices, such as dynamic random accessmemories (DRAM), include multiple metal routing layers. These layers areoften referred to as Metal 1 to Metal N, where Metal 1 is the firstmetal layer formed. Because the metal interconnect extends below anactive region 116 of the substrate it can be accessed by removing aportion of the back surface 118 of the semiconductor device. It is notedthat a top region 120 of the metal interconnect 110 is terminated in ahorizontal plane located below a plane of the Metal N layer 114. Abottom region 122 of the metal interconnect is exposed through thesemiconductor substrate 108 (after section 118 is removed) to provide anelectrical path through the substrate. The illustration of FIG. 1 hasbeen simplified to focus on the location of the metal interconnectrelative to the routing layer. Those skilled in the art will appreciatethat a semiconductor device includes additional circuitry and processfabrication steps that have not been illustrated or descried herein.

Referring to FIGS. 2 through 14, integration processes according toembodiments of the present invention are described. FIG. 2 illustrates across-section of an in-process semiconductor device 200 fabricated on asilicon substrate 201. The device includes transistors 202 having gates204 and source/drain implant regions 206. A vertical contact 210 extendsthrough multiple layers of material, such as dielectric layers 212, 214,216 and 218, to provide an electrical interconnect to a source/drainimplant region 206. For purposes of understanding the invention, detailsof the transistors, multiple dielectric layers and the contact are notrequired. Further, the present invention is not limited to a specificsemiconductor device. For example, the transistors 202 illustrated areplanar transistors and embodiments of the invention are equally usefulin devices having vertical or three-dimensional transistors. In oneembodiment the semiconductor device is a volatile memory, such as adynamic random access memory (DRAM), and the transistors can be accesstransistors used to access a charge storage node such as a capacitor(not illustrated).

At a fabrication point following formation of the transistors, a lowdielectric constant barrier and etch stop film 220, such as BLOkTMmaterial from Applied Materials, Inc., Santa Clara, Calif., is depositedon a top surface of the device. Referring to FIG. 3, a photo resistmaterial 224 is deposited, patterned and selectively removed using wellknown photo resist processes to provide an opening 230. Because thepatterned opening will be used to form conductive vias, the geometricshape of the opening is not critical. In general, the shape as viewedfrom above (plan view) can be round, oval, square, diamond, rectangularor any other appropriate multi-sided shape.

Etch processing is then performed to selectively remove layers ofmaterial located between the photo resist 224 and the silicon substrate201, see FIG. 4. A portion of the silicon substrate 201 is also removedthrough etching, see FIG. 5, to form via 234 into the silicon substrate.The etching operation may be completed in multiple steps. For example,if the intermediate layers between the photo resist 224 and silicon 201are oxide layers, an oxide etch can be performed to expose the siliconsubstrate 201 and then a silicon etch can be performed. Any suitableetch process can be used, including but not limited to: dry etching“Bosch” style, steady state style, cryogenic silicon etch, laserablation, particle blasting, wet etching, and micro electro dischargemachining. In one embodiment the cross sectional width of the via isapproximately 10 um and the depth of the silicon etch is between 50 and100 um. As such an aspect ratio of about 5:1 to 10:1 may be desirable insome embodiments. Actual aspect ratios, however, will be dependent uponthe specific semiconductor device being fabricated. The via 234 extendsinto the silicon substrate to a depth that is below an active region ofthe top of the substrate. The active region can be considered the regionof the silicon substrate containing circuit features, such as dopantimplant regions, and regions of the bulk silicon substrate required forproper operation of the semiconductor device.

As illustrated in FIG. 6, the photo resist layer 224 is removed and anoxide layer 240 is deposited over the barrier layer 220 and into theetched via 234 following removal of the photo resist. The oxide layerprovides a dielectric, or insulation layer between a metal interconnectto be formed in the via and the silicon substrate 201. A second barrierlayer 244, such as Ta, W, TiN or TiW or other suitable material, isformed over the oxide 240 and then a metal seed layer 250 is deposited.The metal seed layer in one embodiment is a copper seed layer, inanother embodiment the seed layer is Tungsten or other suitablematerial. For purposes of describing the present invention the detaileddescription will describe a device using copper as the metal. The termmetal as used herein includes materials having overlapping conductionbands and valence bands, including but not limited to metals of thePeriodic Table and alloys thereof. Those skilled in the art with thebenefit of the present description will appreciate that the invention isnot limited to copper embodiments. The seed layer can be formed usingtechniques such as CVD (Chemical Vapor Deposition), PVD (Physical VaporDeposition), electro graphing, or plating on the barrier. The seed layerin one embodiment has a general thickness in the range of 2-6 kangstrom.

After the seed layer 250 is deposited, a plating mask 252 is fabricatedas illustrated in FIG. 7. Any plating mask material that is formed inthe etched via is removed to expose the seed layer in via 234. Theplating mask can be patterned using either a negative or positive photoresist. It is believed that the negative photo resist material can bemore completely removed from the via. Other surface plating inhibitorscan be used as the plating mask. For example, stamped on material orsputtered layers such as Ti could be used.

A plating process is then performed to fill the via with solid metal254, as shown in FIG. 8. For example, a copper plating process isperformed to fill the via. In one embodiment a electrochemicaldeposition (ECD) plating process is used. Other plating processes andmaterials could be used, such as CVD, PVD, electroless (chemical orauto-catalytic), nano-particle or conductive polymers.

Depending upon the aspect ratio of the via, the plating process may needto be optimized by one skilled in the art to avoid and/or reduce thecreation of voids in the metal. It is noted that the plating mask layer252 limits the plating process to the seed layer exposed in the via.That is the horizontal regions of the seed layer outside the via remainselectively covered to prevent plating.

After the plating mask 252 is removed a planarizing process is performedto remove the protected seed layer 250 and plated metal 254 extendingvertically above the dielectric layer 240, see FIG. 9. For example, achemical mechanical planarizing (CMP) operation can be performed thatstops on the oxide layer 240. Following the planarization operation anoptional capping layer 260 can be formed as illustrated in FIG. 10. Thecapping layer can be an oxide or other barrier layer to prevent metalmigration. This capping layer is particularly useful in helping tocontain metal 254 and avoid contamination of fabrication equipment usedin subsequent processing operations. For example, it is known thatcopper is highly mobile and once process equipment is exposed to copperit is often limited to future use in operations employing copper.

Multiple operations are illustrated as having been completed at theprocess point in FIG. 11. Specifically, a damascene process is performedon the device by patterning a photo resist (not shown), etching toselectively expose contact 210, forming a metal 1 routing layer 300 inthe etched opening, and planarizing the metal 1 layer to a level of thecapping layer 260. The metal 1 layer can be fabricated using a secondseed layer. In this embodiment a top region of the metal interconnect254 is generally in the same horizontal plane as the metal 1 layer 300.Referring to FIG. 12, a dielectric layer 310 is formed after the metal 1layer. Portions of the dielectric layer are then etched to form openings312 to expose contact regions of the metal 1 routing layer 300 and themetal interconnect 254. The size, shape and number of contact opening tothe metal 1 and metal interconnect can vary based upon the needs of theintegrated circuit device. As illustrated, one embodiment can includemultiple openings for contact to the metal interconnect.

Referring to FIG. 13, a metal 2 routing layer 320 has been formed. Itwill be appreciated that to form the metal 2 layer a seed layer (notshown) was formed, the seed layer was plated to fill a recess formed inthe dielectric layer 310, and a planarizing operation was performed toremove excess metal. The top region of the metal interconnect 254 can bedescribed as being in a horizontal plane that is below a primaryhorizontal plane of the metal 2 layer 320. That is, although the metal 2layer contacts the metal interconnect, the primary horizontal plane ofthe metal 2 routing layer is separated vertically from the conductor bya dielectric region.

Additional process steps, not shown, can be performed above the metal 2layer, including the formation of additional dielectric and metalrouting layers. The semiconductor substrate is thinned using techniquesknown to those skilled in the art, such as by back grinding, to expose alower region 340 of the metal interconnect 254, see FIG. 14. Asemiconductor device therefore has been formed having a top side and aback side. A first metal layer 300 is located between the top side andthe back side, and a second metal layer 320 is located between the firstmetal layer and the top side. A metal interconnect 254 extendsvertically through a portion of the semiconductor device to the backside and a top region of the metal interconnect is located verticallybelow a horizontal plane containing the second metal layer 320.

In one embodiment the semiconductor device is fabricated by etching avia into a semiconductor substrate, filling the via with a metalmaterial, forming a metal routing layer subsequent to filling the via,and removing a portion of a bottom of the semiconductor substrate toexpose a bottom region of the metal filled via. Further embodiments caninclude fabricating a transistor having a gate and source/drain implantregions extending into a top region of a silicon substrate. A dielectriclayer is formed above the transistor and a via is then formed throughthe dielectric layer and into the silicon substrate laterally adjacentto the transistor. The via vertically extends below source/drain implantregions of the transistor. A first dielectric layer is formed in theetched via and then a metal seed layer is formed after the firstdielectric layer. A blocking layer is formed over selected regions ofthe seed layer located outside of the via and the exposed regions of theseed layer are plated to fill the via with metal and form a metal plug.The blocking layer and unplated seed layer are removed and a seconddielectric layer is formed over the metal plug. A metal routing layer isthen formed over the second dielectric area, such that the metal routinglayer contacts the metal plug through the second dielectric layer toform an electrical connection.

It will be appreciated by those skilled in the art with the benefit ofthe present disclosure that the process steps described above can bemodified without departing from the invention. That is, processintegration changes can be made to adapt to equipment, semiconductordevice parameters and process concerns of a manufacturer.

Referring to FIGS. 15-16, alternate embodiments are illustrated. Inthese embodiments the damascene process used to form the metal routinglayers are used to enable electrical direct contact between the metal 1layer and the metal interconnect directly. For example, as shown in FIG.15 the etch operation exposed the metal interconnect 254 and removed thebarrier layer on the vertical sides of the seed layer 250 so that metal1 layer 400 contacts the interconnect. After planarization the metal 1layer is integrally connected to the metal interconnect. Alternately,the etch operation can expose the metal interconnect 254 and removed thebarrier layer on the vertical and top sides of the interconnect so thatmetal 1 layer 410 contacts the interconnect 254 on the top surface, seeFIG. 16.

Alternative embodiments of the present invention include forming themetal interconnect following formation of a metal routing layer, butprior to formation of a final metal routing layer. In addition, metalinterconnects can be formed between the formation of metal layers. Thatis, the invention is not limited to one metal interconnect formationoperation.

Embodiments of the invention are not limited to two metal routinglayers. Further, a portion of any, some, or all of the metal routinglayers can be electrically connected to the metal interconnect. That is,a semiconductor device may include hundreds of metal interconnects eachdesignated for a different operational purposes. Therefore theelectrical path(s) of the interconnects can and most likely will bedifferent.

FIG. 17 illustrates a redistribution layer 500 which can include ballbond pad location(s) 510 is formed on the back, or bottom, of thesemiconductor substrate following exposure of the metal interconnect254. The redistribution layer forms electrical and physical contact withthe interconnect. Fabrication processes for thinning a semiconductorwafer and forming redistribution layers are well known in the art. Assuch a detailed description is not provided herein.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe disclosure will be apparent to those of ordinary skill in the art.Accordingly, this application is intended to cover any adaptations orvariations of the disclosure.

1-8. (canceled)
 9. A method of fabricating a semiconductor devicecomprising: etching a via into a silicon substrate from a first sidetoward a second side of the silicon substrate; forming a conductiveinterconnect in the etched via, the conductive interconnect having afirst end proximate the first side of the silicon substrate and a secondend proximate the second side of the silicon substrate; insulating theconductive interconnect with a first dielectric material proximate thefirst side of the silicon substrate; forming a first metal routingstructure on the first dielectric material, the first metal routingstructure being at least partially in the first dielectric material;insulating the conductive interconnect and the first metal routingstructure with a second dielectric material; forming a plurality ofopenings in the second dielectric material, the openings including afirst opening generally corresponding to the first metal routingstructure, a second opening generally corresponding to the conductiveinterconnect, and a third opening generally corresponding to a secondmetal routing structure; and filling the plurality of openings with aconductive material, thereby forming a first conductive path between thefirst and second metal routing structures, a second conductive pathbetween the second metal routing structure and the conductiveinterconnect, and the second metal routing structure.
 10. The method ofclaim 9, further comprising: forming an insulating material in theetched via; forming a seed material on the insulating material; blockingselected regions of the seed material located outside of the via with aphotoresist; and plating exposed regions of the seed material to fillthe via with a conductive material, thereby forming the conductiveinterconnect.
 11. The method of claim 9, further comprising: fabricatinga transistor having a gate and source/drain implant regions in thesilicon substrate.
 12. The method of claim 11, further comprising:forming an insulating material on the silicon substrate with thefabricated transistor; and forming a contact coupled to the transistor.13. The method of claim 12, further comprising etching the via into thesilicon substrate laterally adjacent to the transistor.
 14. The methodof claim 12, further comprising extending the via deeper into thesilicon substrate than the source/drain implant regions of thetransistor.
 15. The method of claim 12, further comprising forming thecontact generally parallel to the conductive interconnect.
 16. Themethod of claim 9, further comprising forming the first conductive pathgenerally parallel to the second conductive path.
 17. The method ofclaim 9, further comprising forming the first conductive path generallyparallel to the conductive interconnect.
 18. The method of claim 9,further comprising forming the second conductive path generally parallelto the conductive interconnect.
 19. The method of claim 9, furthercomprising forming the second metal routing structure generallyperpendicular to the conductive interconnect.
 20. The method of claim 9,further comprising forming the second metal routing structure generallyparallel to the first conductive path.
 21. The method of claim 9,further comprising forming the second metal routing structure generallyparallel to the second conductive path.
 22. The method of claim 9,further comprising forming the first metal routing structure laterallyspaced apart from the conductive interconnect.
 23. The method of claim9, further comprising: removing a portion of the second side of thesilicon substrate to expose the second end of the conductiveinterconnect; and forming a conductive redistribution structureproximate the second side of the silicon substrate and electricallycoupled to the conductive interconnect.
 24. The method of claim 23,wherein the conductive redistribution structure comprises a conductiveball bond pad.
 25. The method of claim 9, wherein the conductiveinterconnect has a length to width ratio of about 5:1 to 10:1.
 26. Amethod of fabricating a semiconductor device comprising: etching a viainto a silicon substrate from a first side toward a second side of thesilicon substrate; forming a conductive interconnect in the etched via,the conductive interconnect having a first end proximate the first sideof the silicon substrate and a second end proximate the second side ofthe silicon substrate; insulating the conductive interconnect with afirst dielectric material proximate the first side of the siliconsubstrate; forming a first metal routing structure on the firstdielectric material, the first metal routing structure being at leastpartially in the first dielectric material; insulating the conductiveinterconnect and the first metal routing structure with a seconddielectric material; forming a first opening generally corresponding tothe first metal routing structure; forming a second opening generallycorresponding to the conductive interconnect; filling the first openingwith a conductive material to form a first conductive path; filling thesecond opening with the conductive material to form a second conductivepath generally parallel to the first conductive path; electricallycoupling the first conductive path and the second conductive path via asecond metal routing structure.
 27. The method of claim 26, furthercomprising: forming a third opening generally perpendicular to the firstconductive path and the second conductive path; filling the thirdopening with the conductive material to form the second metal routingstructure.
 28. The method of claim 26, further comprising: removing aportion of the second side of the silicon substrate to expose the secondend of the conductive interconnect; and forming a conductiveredistribution structure proximate the second side of the siliconsubstrate; electrically connecting the conductive redistributionstructure with the conductive interconnect.
 29. The method of claim 26,wherein the conductive redistribution structure comprises a conductiveball bond pad.